A computer store has 75 printers of which 25 are laser printers and 50 are ink jet printers. If a group of 10 printers is chosen at random from the store, find the mean and variance of the number of ink jet printers.
A) Mean = 6.7, Variance = 2.2
B) Mean = 6.7, Variance = 1.5
C) Mean = 3.3, Variance = 2.2
D) Mean = 3.3, Variance = 1.5

Question

Quizplus · Accepted Answer

The mean number of ink jet printers in a group of 10 is calculated using the formula for the mean of a hypergeometric distribution: (n * K) / N = (10 * 50) / 75 = 6.7. The variance is calculated using the formula: [n * (K/N) * (1 - K/N) * (N-n)/(N-1)] = [10 * (50/75) * (25/75) * (65/74)] = 2.2.

A Computer Store Has 75 Printers of Which 25 Are